运行时和编译时的区别是什么?
当前回答
编译时和运行时之间的差异就是精明的理论家所说的阶段差异的一个例子。它是最难学习的概念之一，特别是对于没有太多编程语言背景的人来说。要解决这个问题，我发现问一下很有帮助
程序满足哪些不变量? 在这个阶段会出现什么问题? 如果阶段成功，后置条件是什么(我们知道什么)? 输入和输出是什么(如果有的话)?
编译时
The program need not satisfy any invariants. In fact, it needn't be a well-formed program at all. You could feed this HTML to the compiler and watch it barf... What can go wrong at compile time: Syntax errors Typechecking errors (Rarely) compiler crashes If the compiler succeeds, what do we know? The program was well formed---a meaningful program in whatever language. It's possible to start running the program. (The program might fail immediately, but at least we can try.) What are the inputs and outputs? Input was the program being compiled, plus any header files, interfaces, libraries, or other voodoo that it needed to import in order to get compiled. Output is hopefully assembly code or relocatable object code or even an executable program. Or if something goes wrong, output is a bunch of error messages.
运行时
We know nothing about the program's invariants---they are whatever the programmer put in. Run-time invariants are rarely enforced by the compiler alone; it needs help from the programmer. What can go wrong are run-time errors: Division by zero Dereferencing a null pointer Running out of memory Also there can be errors that are detected by the program itself: Trying to open a file that isn't there Trying find a web page and discovering that an alleged URL is not well formed If run-time succeeds, the program finishes (or keeps going) without crashing. Inputs and outputs are entirely up to the programmer. Files, windows on the screen, network packets, jobs sent to the printer, you name it. If the program launches missiles, that's an output, and it happens only at run time :-)
其他回答
public class RuntimeVsCompileTime {
public static void main(String[] args) {
//test(new D()); COMPILETIME ERROR
/**
* Compiler knows that B is not an instance of A
*/
test(new B());
}
/**
* compiler has no hint whether the actual type is A, B or C
* C c = (C)a; will be checked during runtime
* @param a
*/
public static void test(A a) {
C c = (C)a;//RUNTIME ERROR
}
}
class A{
}
class B extends A{
}
class C extends A{
}
class D{
}
嗯，好吧，运行时是用来描述程序运行时发生的事情。
编译时间用来描述在构建程序(通常由编译器)时发生的事情。
例如:在强类型语言中，类型可以在编译时或运行时检查。在编译时，这意味着如果类型不兼容，编译器将报错。在运行时，意味着你可以很好地编译你的程序，但在运行时，它会抛出一个异常。
作为其他答案的补充，以下是我对外行的解释:
您的源代码就像一艘船的蓝图。它定义了船应该如何制造。
如果你把你的蓝图交给造船厂，他们在建造船的时候发现了一个缺陷，他们会立即停止建造并向你报告，在船离开干船坞或接触水之前。这是一个编译时错误。这艘船甚至从未真正漂浮过，也没有使用过它的引擎。这个错误之所以被发现，是因为它甚至阻止了这艘船的制造。
当您的代码编译完成时，就像船完成了一样。建好了，可以出发了。当你执行你的代码时，就像在航行中让船下水一样。乘客上了船，引擎在运转船体在水面上，这是运行时间。如果你的船有致命的缺陷，在处女航时就沉没了(或者可能是一些额外的麻烦)，那么它就遇到了运行错误。
编译时间:您作为开发人员编译代码的时间段。
运行时间:用户运行你的软件的时间段。
你需要更明确的定义吗?
